A gas turbine has a plurality of combustors disposed in a toroidal form, and is arranged to flow combustion gases of these combustors to turbine blade (stationary blade and moving blade) portions of a turbine body, thereby rotating the turbine body. During the operation of the gas turbine, all the combustors need to act normally.
During the operation of the gas turbine, therefore, it is necessary to keep watch on whether an abnormality, such as misfire or fuel injection nozzle obstruction, occurs or not in one or more of the combustors. If it is judged that the abnormality has occurred in the combustor, it is necessary to effect automatic stop or tripping of the gas turbine, thereby protecting the gas turbine.
For this purpose, thermocouples, the number of which is the same as or larger than the number of the combustors, are arranged toroidally at the outlets of the turbine blades (downstream in the flowing direction of the combustion gases) (see FIGS. 1(a), 1(b); details to be offered later), and these thermocouples measure the temperatures of the combustion gases at the outlets of the turbine blades (blade pass temperatures). Based on the measured values of the blade pass temperatures of the thermocouples, a gas turbine protection apparatus outputs a gas turbine automatic stop signal or a gas turbine tripping signal as a gas turbine protection signal. If the gas turbine automatic stop signal is outputted from the gas turbine protection apparatus, a fuel supply system gradually decreases a fuel to be supplied to the combustors to reduce a load, thereby bringing the gas turbine body to an automatic stop. If the gas turbine tripping signal is outputted from the gas turbine protection apparatus, the fuel supply system instantaneously cuts off fuel supply to the combustors, tripping (urgently stopping) the gas turbine.
If an abnormality occurs in any one of the combustors, only the blade pass temperature corresponding to the abnormal combustor has a great deviation (difference from the average value) or a large deviation change amount (change rate) in comparison with the blade pass temperatures corresponding to the other combustors. Thus, the abnormality of the abnormal combustor can be detected. Hence, the gas turbine protection apparatus has an interlock logic which outputs the gas turbine automatic stop signal or the gas turbine tripping signal when the blade pass temperature deviation obtained from the blade pass temperature measured value of any of the thermocouples has exceeded a blade pass temperature deviation great set value, or when the change amount of the blade pass temperature deviation has exceeded a blade pass temperature deviation change amount large set value.
The blade pass temperature of the combustion gas of each combustor is not measured at the turbine blade outlet position corresponding to each combustor, but is measured at the turbine blade outlet position at an angle displaced from each combustor in the rotating direction of the turbine body and in the circumferential direction by several of the combustors. This displacement for the blade pass temperature is called a swirl angle and, for example, is equivalent to 2.7 of the combustors, although it differs according to the magnitude of the load. If the swirl angle is equivalent to 2.7 of the combustors, the blade pass temperature of the combustion gas of the abnormal combustor is measured not by the thermocouple disposed at the turbine blade outlet position corresponding to the abnormal combustor, but by the thermocouple disposed at the turbine blade outlet position displaced from the former thermocouple in the circumferential direction by the equivalent of 2 or 3 of the combustors.
Patent Document 1 discloses an example in which the blade pass temperature of a combustion gas of a combustor was measured by a thermocouple disposed at a turbine blade outlet, and the measured value of the blade pass temperature of this thermocouple was used for gas turbine control.
Patent Document 1: Japanese Patent Application Laid-Open No. 1994-264761